[very common; historically, ‘according to religious
law’] The usual or standard state or manner of something. This word
has a somewhat more technical meaning in mathematics. Two formulas such as
9 + x and x +
9 are said to be equivalent because they mean the same
thing, but the second one is in canonical
form because it is written in the usual way, with the highest
power of x first. Usually there are fixed
rules you can use to decide whether something is in canonical form. The
jargon meaning, a relaxation of the technical meaning, acquired its present
loading in computer-science culture largely through its prominence in
Alonzo Church's work in computation theory and mathematical logic (see
Knights of the Lambda Calculus). Compare
vanilla.

Non-technical academics do not use the adjective
‘canonical’ in any of the senses defined above with any
regularity; they do however use the nouns canon and canonicity (not **canonicalness or
**canonicality). The canon of a given
author is the complete body of authentic works by that author (this usage
is familiar to Sherlock Holmes fans as well as to literary scholars).
‘The canon’ is the body of works in a
given field (e.g., works of literature, or of art, or of music) deemed
worthwhile for students to study and for scholars to investigate.

The word ‘canon’ has an interesting history. It derives
ultimately from the Greek
κανον (akin to the
English ‘cane’) referring to a reed. Reeds were used for
measurement, and in Latin and later Greek the word ‘canon’
meant a rule or a standard. The establishment of a canon of scriptures
within Christianity was meant to define a standard or a rule for the
religion. The above non-techspeak academic usages stem from this instance
of a defined and accepted body of work. Alongside this usage was the
promulgation of ‘canons’ (‘rules’) for the
government of the Catholic Church. The techspeak usages (“according
to religious law”) derive from this use of the Latin
‘canon’.

Hackers invest this term with a playfulness that makes an ironic
contrast with its historical meaning. A true story: One Bob Sjoberg, new
at the MIT AI Lab, expressed some annoyance at the incessant use of jargon.
Over his loud objections, GLS and RMS made a point of using as much of it
as possible in his presence, and eventually it began to sink in. Finally,
in one conversation, he used the word canonical in jargon-like fashion without
thinking. Steele: “Aha! We've finally got you talking jargon
too!” Stallman: “What did he say?” Steele: “Bob
just used ‘canonical’ in the canonical way.”

Of course, canonicality depends on context, but it is implicitly
defined as the way hackers normally expect things to
be. Thus, a hacker may claim with a straight face that ‘according to
religious law’ is not the canonical meaning of
canonical.